Miniaturization is a challenge for manufacturers of electronic products. To build smaller electronic products, the components of the electronic products may also require miniaturization. Thus, manufacturers of electronic components, such as integrated circuit (IC) chips, are under constant pressure to increase the density of features in a given area of a chip.
In an attempt to fabricate smaller chips having more features, manufacturers have kept reducing the wavelength of the light and increased the numerical aperture of the projection optics used to image the circuit features on a wafer. Optical proximity corrections and phase shifting techniques have been widely adopted in mask pattern generation to improve resolution. With critical dimensions of some features now significantly less than half of a wavelength and the currently used numerical aperture being close to one, further miniaturization may become increasingly difficult.